FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in the prior art. Wireless telecommunications system 100 comprises: mobile station 101, base transceiver stations 102-1, 102-2, and 102-3 (collectively or generically referenced as “102”), base station controller 103, and mobile switching center 111. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in accordance with the Global System for Mobile Communications (GSM) set of standards and in well-known fashion.
Base transceiver station (BTS) 102 is mobile station 101's access point to system 100. The BTS performs speech encoding, encryption, and other functions. Communications between mobile station 101 and a BTS 102 occur over an air interface. These communications, which include control information as well as voice/data, are carried over traffic channels via known methods.
One or more control channels are used to establish and maintain communications between BTS 102 and mobile station 101. The control channel also carries reports of measurements recently made by mobile station 101. The network measurement report, or “NMR,” for any given mobile station 101 includes measurements of the received signal strength of the control channels associated with each BTS that is currently in range of that mobile station. This measurement is commonly referred to as a received signal strength indication (“RSSI”). The NMR includes the identity of the mobile station making the measurements, a set of RSSI measurements and, for each RSSI measurement, the identity of the BTS with which it is associated. System 100 can include a different number of BTSs than that depicted.
Base station controller (BSC) 103 controls multiple BTSs. For example, the BSC handles radio channel allocation, frequency administration, receives power and signal measurements originating from the mobile stations, and controls handovers between BTSs coupled to the same BSC. As depicted in FIG. 1, BSC 103 controls BTS 102-1 through 102-3. Although BSC 103 is depicted as being geographically remote from the BTSs 102, it can be co-located with any of the BTSs or with the mobile switching center 111. System 100 can include multiple BSCs.
The interface between BSC 103 and each BTS 102 is known as the “Abis” link or interface. The communications carried over the Abis link include both voice/data information and control information. These communications are carried over a traffic channel and a signaling channel. The Abis link carries the NMRs originating from mobile station 101 communicating with each BTS 102-1 through 102-3 controlled by BSC 103.
Mobile switching center (MSC) 111 provides at least some of the switching capability across system 100. MSC 111 comprises a switch that orchestrates the provisioning and control of telecommunications service to the mobile stations. System 100 can include a plurality of MSCs, each responsible for a large geographic portion of the network. MSC 111 can be connected to multiple BSCs, and it can interface with other MSCs. The interface between the mobile switching center and each base station controller is called the “A” link or interface.
MSC 111 also enables a subscriber of system 100 to place a call to, or receive a call from another network, such as the Public Switched Telephone Network (PSTN) or other wireless networks.
It is known that information contained in an NMR, or otherwise reported to BTS 102 by mobile station 101, can be used, via any of various techniques, to determine or estimate the location of the reporting mobile station. Such information can include, for example, information that directly indicates the geographic location of a wireless mobile station, such as latitude/longitude data, or other processed Global Positioning System (GPS) data, or a street address. Such information can also include indirectly related data, such as raw GPS coordinates or RSSI data. A convenient place to obtain such data in system 100 is at the Abis links between BSC 103 and BTSs 102, such as via the use of taps or probes.
Since the late 1990s, there have been proposals to tap data from the Abis links. The tapped information is typically used to provide location information about a specific mobile station. One such proposal is presented in U.S. Pat. No. 7,783,299, which is referred to hereinafter as the “'299 patent.”
The '299 patent presents a method and system whereby certain signaling links, such as the Abis link, are monitored for a predefined “trigger.” If the trigger is detected, then a predefined location service is initiated, such as a location service that determines the location of the mobile station that is associated with the triggering event. For example, the trigger can be the identifier for a particular mobile station, a 9-1-1 call, etc.
FIG. 2 depicts an embodiment of system 200 disclosed in the '299 patent, while FIG. 3 depicts method 300 by which system 200 operates. The system is based on GSM network architecture and comprises mobile station 101, BTS 102-1, 102-2, and 102-3, BSC 103, and MSC 111. Probes 204-1, 204-2, and 204-3 are electrically coupled to the Abis links between BSC 103 and BTS 102-1, 102-2, and 102-3, respectively. Probes 204-1 through 204-3 are capable of monitoring the Abis links for certain triggers.
In accordance with process 301 of method 300, triggers are defined. As an illustration of the method, it is assumed that there are two triggers: (1) a 9-1-1 call and (2) the predetermined identifier of a mobile station of interest.
In accordance with process 302, probes 204-1 through 204-3 commence monitoring the Abis links.
In accordance with process 303, a determination is made as to whether a predefined trigger is detected on one of the Abis links. If not, the probes continue to monitor for a predefined trigger. On the other hand, if a predefined trigger is detected, then control proceeds to process 304.
As a first example, when mobile station 101 originates a 9-1-1 call via BTS 102-1, probe 204-1 detects that call as a triggering event (i.e., detects that the dialed digits field contains “9-1-1”). Relevant information concerning mobile station 101 is directed to location application 215 so that the location of that mobile station is determined in accordance with process 304. The location of mobile station 101 is then reported to an interested party (e.g., the police, etc.).
As a second example, when mobile station 101 having the predetermined identifier originates a call via BTS 102-2, probe 204-2 identifies this call as a triggering event, and relevant information is directed to location application 215. The location of mobile station 101 is determined per operation 304 and then reported to an interested party (e.g., homeland security, etc.).
In contrast to the foregoing examples, when mobile station 101 places a call, but neither is originating a 9-1-1 call nor has the predetermined identifier, then no triggering event is detected at operation 303. Consequently, location determination based on the predefined triggers is not initiated in this case.